Can you use vertex Weight as falloff?
Welcome to Stackexchange! You are trying to transform polygons based on weights of vertices, so your current approach wont work as you expected.

Instead, you need to somehow compute a weight for each polygon based on the vertices that make it. One way is to take the average of the weights of the vertices of each polygon. To do so, loop over the polygon indices, get the weights at those indices and average them:



Then you can use the Offset Polygons node to transform the polygons based on the custom falloff just as you did. There is no need to extract the polygon info or recreate it, the Offset Polygons node takes care of this: